The present invention relates to a semiconductor design technique, and more particularly, an internal signal monitoring device in a semiconductor memory device and a method for monitoring the same.
A semiconductor memory device transmits data read from a memory cell to an input/output pad (DQ pad) through various internal signals. At this time, there is the problem that the data is distortedly transmitted or is not transmitted due to diverse factors. One of the factors is a distortion of the internal signals, which is monitored by observing operational states of the internal signals based on whether the data as desired is or not actually output to the input/output pad. When the desired data is not output, different types of tests are performed to compare the desired data and an actual output data and to try to find a doubtful internal circuit. Further, an oscilloscope connected to a device such as a Pico-probe, or an expensive internal signal probing device is used to read out the internal signals, thereby detecting that something is wrong with the internal signals.
However, using the oscilloscope connected to the pico-probe or the internal signal probing device requires great skill compared to a simple task of determining a pass/fail of data output.
Moreover, signals actually used in the semiconductor memory device, which are output signals from a small driver stage constructed in a semiconductor chip, become distorted when an external device such as the Pico-probe is directly contacted to a node to be inspected for the purpose of monitoring such internal signals. Thus the internal signals and operational states thereof cannot be exactly monitored. In addition, since an interconnection in the semiconductor chip is typically enclosed with a protective coating, a prior process to remove the protective coating is required for monitoring the internal signals. For example, FIG. 1 shows a block diagram illustrating a conventional internal signal monitoring device in the semiconductor memory device.
Moreover, because a semiconductor chip is typically packaged and such a packaged semiconductor chip should be dismantled in order to monitor the internal signals through the Pico-probe or the internal signal probing device, it is difficult to monitor the internal signals in the packaged semiconductor chip.